Orthopaedic implants and methods

ABSTRACT

There is provided a tibial component comprising: a tibial tray with an inferior side; and a support member connected to the inferior side of the tibial tray, the support member having a stem portion, the support member further comprising at least one opening. In one embodiment, the at least one opening is constructed and arranged to receive a sawblade or an osteotome. In another embodiment, the at least one opening is comprised of solid material but is radio-lucent. In yet another embodiment, the at least one opening is comprised of solid material and is frangible.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/209,997, filed Aug. 15, 2011 and issued as U.S. Pat. No. 10,034,756,which claims the benefit of U.S. Provisional Application No. 61/373,606,filed Aug. 13, 2010 and U.S. Provisional Application No. 61/373,783,filed Aug. 13, 2010. The disclosure of each prior application is herebyincorporated by reference in its entirety.

RELATED FIELDS

Orthopaedic implants and methods involving the same, such as, but notlimited to, orthopaedic implants and methods for the proximal tibia,such as tibial trays that may include one or more of a keel and/or astem and methods for revising the same.

BACKGROUND

There are several factors that are potentially relevant to the designand performance of orthopaedic implants. In the example of a tibialtray, a non-exhaustive list of such factors includes the implant'sflexibility (or the flexibility of certain portions of the implant orits flexibility about certain axes or other constructs), which mayindicate the degree to which the tray will conform to the potentiallyuneven resected surfaces of a proximal tibia; the implant's rigidity (orthe rigidity of certain portions of the implant or its rigidity aboutcertain axes or other constructs), which may indicate the degree towhich stresses or other forces imposed by the bony and other anatomyassociated with the knee joint will be transmitted to the peripheralhard cortical shell of the proximal tibia; the implant's resistance torotation; the amount of bone preserved; and/or other potentiallyrelevant factors. In some instances, accommodation of these or otherfactors may require trade-offs to balance competing factors. In someinstances, one or more of these factors will not be considered or givena high level of importance to the design of an orthopaedic implant.

Some known tibial trays include a fin or a keel that may increase thestrength of the implant while also helping to prevent rotation relativeto the bone. In some instances, such fins or keels may present certaindrawbacks. For instance, in some cases, the fin or keel may impede thevisualization of the implant and surrounding anatomy using x-ray orother imaging technologies. For instance, it may be desirable in somecases to visualize the implant and its surrounding anatomy, includingthe surrounding bony anatomy, by taking one or more x-rays in planessuch as coronal and sagittal planes or in other planes to assess whetherthe implant may be loosening over time. Such loosening might beindicated by lucent lines appearing in the x-ray image around portionsof the implant or other indications that the bone has receded from theimplant or otherwise has become loose. In some instances, a fin or keelof the implant may obstruct the ability to view such lucent lines or mayotherwise hinder the evaluation of the image. Other orthopaediccomponents might feature these or other structures similarly impairingvisualization of the implant in the bone and other anatomy.

Some known tibial trays are difficult to remove or revise. For somerevision procedures, it is necessary to cut around the existing implantor otherwise position instrumentation about the implant to loosen itfrom the surrounding bone and/or other anatomy before removal. In someinstances, particularly, for instance, some instances where the implantis a tibial tray having a keel, it may be difficult to cut aroundcertain portions of the keel or otherwise access certain areas of thebone-implant interface to loosen the implant. It may be particularlydifficult, for instance, to access certain areas of the bone-implantinterface depending on the surgical approach taken. For instance, if ananterior-medial incision is used to access the knee joint, the keelstructure may impede a surgeon's access to posterior-lateral portions ofthe bone-implant interface. In such instances, removal of the implantmay undesirably require excessive or unintended bone removal as well.

In some instances, stability or fixation of the implant, such as atibial tray or other implant, in the bone may be of some significance.For instance, the distribution of “hard” versus “soft” bone is notalways uniform or predictable, and, in some instances, during bonepreparation a punch, drill or other instrument may penetrate the bone atan undesired angle or position since it may tend to follow the path ofleast resistance into softer bone. Moreover, in some instances, such assome tibial cases, distal metaphyseal bone may tend to be spongier andsofter than proximal metaphyseal bone. In some implant cases, it may bedifficult to achieve adequate fixation or other stability in the distalmetaphyseal bone. Moreover, with some implants, including some tibialimplants, there may be a tendency over time for the implant to subsideor migrate.

SUMMARY

There is provided a tibial component comprising: a tibial tray with asuperior side and an inferior side; and a support member connected tothe inferior side of the tibial tray, the support member having a stemportion, the support member further comprising at least one opening. Inone embodiment, the stem portion slants at an angle relative to theinferior surface. In another embodiment, the stem portion has a proximalend and a distal end, and the proximal end is connected to the inferiorside of the tibial tray. In yet another embodiment, the tibial tray andthe support member are monolithic. In one particular embodiment, thetibial tray and the support member have a male/female arrangement. Inanother embodiment, the tibial component further comprises a porous beadcoating. In still another embodiment, the at least one opening isconstructed and arranged to receive a sawblade or an osteotome. In oneembodiment, the at least one opening is comprised of solid material butis radio-lucent. In yet another embodiment, the at least one opening iscomprised of solid material and is frangible. In another embodiment, thetibial component further comprises a modular stem removably attached tothe stem portion. In one embodiment, the support member includes atleast two arms, and each of said arms defines an opening. In anotherembodiment, the at least two arms are angled relative to one another.

Some of the non-limiting embodiments of tibial trays described hereininclude one or more fins or keels that include or define holes,openings, recesses, areas formed or filled with different materials, orother structures or features. Some of the non-limiting embodiments oftibial trays described herein may additionally or alternatively includea monolithic, modular or otherwise connected fluted stem. The presentapplication is not limited to tibial trays; however, and one of skill inthe art will recognize that at least some of the concepts presentedherein could be applied to other orthopaedic implants.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a top plan view of one non-limiting example of a tibial tray.

FIG. 2 is a rear elevation view of the tibial tray of FIG. 1.

FIG. 3 is a side elevation view of the tibial tray of FIG. 1.

FIG. 4 illustrates a modular stem that may optionally be used with thetibial tray of FIG. 1.

FIG. 5 is a distal view of the modular stem of FIG. 4.

FIG. 6 is a cross-section of the stem of FIG. 4 taken along line 6-6shown in FIG. 5.

FIG. 7 is a cross-section of the stem of FIG. 4 taken along line 7-7shown in FIG. 5.

FIG. 8 illustrates a distal view of an alternative embodiment of flutinguseable with a modular stem such as the modular stem of FIG. 4.

FIGS. 9-14 illustrate schematically an alternative embodiment of atibial tray with a modular stem.

FIG. 15 illustrates a further embodiment having porous beaded coatings.

FIG. 16-19 illustrate alternative embodiments having various stemconfigurations.

FIG. 20-25 illustrate further embodiments to provide components havingporous beaded coatings and methods for their manufacture.

DETAILED DESCRIPTION

FIGS. 1 through 3 illustrate a non-limiting example of a tibialcomponent 100. As shown in FIGS. 2 and 3, the tibial component 100includes support member 110 defining a pair of openings 112. In some,although not necessarily all, embodiments, these openings may be sized,positioned, oriented and otherwise constructed to: (1) reduce by acertain degree the stiffness of the implant while maintaining a certaindegree of strength; (2) facilitate the visualization (such as throughx-ray imaging or other techniques) of lucent lines or other signs thatthe implant is loosening; (3) facilitate the loosening of the tray fromthe bony anatomy in the event resection is necessary, such as byfacilitating the movement of cutting or other types of instrumentationthrough and to the far side of the keel/stem portion that would nototherwise be accessible to the cutter or other instrumentation; and/or(4) facilitate bony-ingrowth or otherwise enhance the stability of theimplant in the bone. In some embodiments, the openings may not featureall of these benefits or may provide other beneficial features.

The support member 110 shown in FIGS. 2 and 3 includes a stem portion114 and two arms 116 extending therefrom. In this particular example,the support member 110 is attached to an underside of a tibial tray 118at three points forming a tripod-like construct. The stem portion 114shown includes a lower cylindrical portion 120 and an upper portion 122that is blended to the arms 116. In the depicted embodiment, the stemportion 114 slants at an angle α and in an anterior-posterior directionas it extends away from an inferior surface 124 of the tray 118;however, in other embodiments, the stem portion 114 may have othergeometries. The stem portion 114 of this particular tibial component 100is located anteriorily on the tray 118, although other locations arealso possible. The arms 116 shown in FIGS. 2 and 3 extend posteriorilyand outwardly from a mid-point of the stem 114 and curve to connect tothe underside of the tibial tray 118. In other embodiments, othernumbers of arms and/or stems in other configurations and geometries canbe employed.

The arms 116 and stem portion 114 of the support member 110 shown inFIGS. 2 and 3 define two openings 112 abutting the inferior surface 124of the tibial tray 118. In other embodiments, different numbers,configurations, shapes, orientations, and positionings of the openingsmay be possible. As discussed below, in some embodiments, the openings112 of the support member 110 may not be “openings” at all in thetraditional sense, but may be areas where other materials or componentsare located, or in which the material forming the tibial component 100has different properties or characteristics.

In some embodiments, the openings 112 formed in the support member 110increase certain flexibility characteristics of the tibial component 100while not overly impinging on a desired strength characteristic of thecomponent. In some embodiments, the openings 112 can be sized and shapedso that the remaining solid material is relatively uniform in shape. Insome embodiments, the remaining solid material is uniform in shape inthe regions of highest stress at the most peripheral edges of the arms116. In some embodiments, the opening size can be configured to be shortenough to allow a sawblade to easily clear material away from the sideswhile being tall enough to allow a thin and narrow osteotome to passthrough in order to facilitate revision surgery. In other embodiments,the openings 112 may be configured to only permit a sawblade or anosteotome, but not both. In some embodiments, such as, for example,where revisability is not a primary goal, taller and deeper openings maybe used to facilitate maximal ingrowth through and around the openings.

In some embodiments, the openings 112 formed in the support member 110provide for better visualization of the tibial component 100, the bonesurrounding the tibial component, and the interface or interfacesbetween the bone and the tibial component 100. The openings 112, in someembodiments, may act as “windows” facilitating the visualization oflucent lines or other visual indications on the imaging data, which maysuggest or indicate that the tibial component is loosening or provideother information for evaluating other issues or concerns. In someembodiments, the size, shape, placement and/or orientation of theopenings 112 can be optimized to facilitate visualization ofbone-implant interfaces and other areas of interest for futurevisualization of the implant after installation. For instance, as shownin the Figures, the openings 112 are primarily oriented in a coronalplane, although, in other embodiments, they could be primarily orientedin a sagittal plane or other orientations. In some embodiments, a widerattachment region with a less abrupt thickness change may be used toprovide for lower stress in the region. In some embodiments, a morenarrow attachment region may be used to increase visibility by lesseningthe amount of material that could block a user's view.

In some embodiments, the openings 112 are not physical openingsextending through the support member 110 or other portion of the tibialcomponent, but may instead be components or areas that do not completelyor partially impair visualization such as by x-ray technologies or othervisualization technologies. For instance, in some embodiments, the“openings” may be filled or may be comprised of materials of lowerdensity (such as materials for facilitating bony in-growth or othermaterials) or that are otherwise semi or completely radio-lucent.

In some embodiments, the openings 112 allow a cutting device or otherinstrument to physically pass through one or more of the openings 112 tofacilitate cutting or otherwise loosening the tibial component from thebone in the event a revision procedure is necessary. In the embodimentshown in FIGS. 2 and 3, the openings 112 are oriented such thatposterior-lateral portions of the bone-implant interface can be accessedby a surgical cutter or other instrument if an anterior-medial approachto accessing the joint space is used. The openings 112 shown in FIGS. 2and 3 also may allow this and other portions of the bone-implantinterface to be accessed from other approaches or directions. In otherembodiments, the position, orientation, size, shape and number ofopenings 112 could be altered to facilitate access to remote portions ofthe bone-implant interface depending on the particular implant involved,the expected surgical approach or approaches that may be utilized,and/or other factors (e.g. the size and shape of the instrument(s) thatmight need to pass through the opening). In some embodiments, the“openings” are not necessarily physical openings through the supportmember 110 but are areas that are frangible or otherwise capable ofbeing relatively-easily penetrated by a surgical instrument to accessthe remote portions of the bone-implant interface if necessary. In someembodiments, the opening(s) could be designed to function as guides forthe instrumentation passing through them, which, in some uses, mightcontrol depth and/or direction of insertion of the instrument (e.g. tolessen chance of damaging surrounding anatomy, such as postero-lateralnerves or arteries) or other aspects of the procedure. In someembodiments, openings 112 can be configured for improved visibility andan ability to approach from anterior to posterior. In some embodiments,the opening(s) 112 could be designed to accommodate surgical cuttinginstruments such as reciprocating or oscillating planar saw bladeshaving cutting edges on either or both of a distal end or one or bothsides, milling bits and other types of rotating cutting devices,chisels, other osteotomes, prying devices, or any other type of surgicalinstrument that might be used for a revision procedure.

As mentioned above, in some embodiments, the openings 112 could befilled with a porous structure or material or otherwise define in-growthsurfaces. In some embodiments, the porous structure or material could beformed from the same material as the rest of the support member 110 buthaving a different porosity, density or other characteristics than otherportions of the support member 110. In some embodiments, the porousstructure is not necessarily confined to the opening 112 and couldoccupy geometric volumes outside of and around other portions of thesupport member 110. Indeed, in some embodiments, the support member 110could function as an internal scaffolding for a volume of bone in-growthmaterial(s) that completely or at least in portions encompass thesupport member 110. In other embodiments, other materials or structuresmay fill the openings 112 and a porous structure or treatment is notnecessary. In some embodiments, the filling material or structure may beintended to facilitate anti-rotation aspects of the implant.

FIG. 1 shows a superior surface 126 of the tibial tray 118, whichincludes attachment feature 128 for receiving and/or securing one ormore articular inserts (not shown) to the tibial tray 118, such insertsdesigned to contact and articulate with a femoral orthopaedic implant(not shown) in use. In the depicted embodiment, the attachment feature128 is a shaped channel to receive and lock-in the articular insert. Inother embodiments, the tibial tray 118 itself may include articularsurfaces and does not require separate articular inserts. The tibialtray 118 shown in FIGS. 1 through 3 includes a posterior notch 130,which may be designed to allow preservation of the attachment site of aposterior cruciate ligament, although, in other embodiments, the tibialtray 118 may or may not include this or other notches or gaps forpreserving one or both of the cruciate ligaments. In other words, thetibial tray, in some embodiments, may be for use in a cruciatesacrificing procedure, a posterior cruciate preserving procedure, or abi-cruciate preserving procedure. In some embodiments, the tibial tray118 may be used for a mobile bearing knee joint or a fixed bearing kneejoint. It will be appreciated that a variety of upper surface andperipheral shapes are possible according to various embodiments and thatsuch shapes can be influenced, at least in part, by strengthrequirements for the tray. For example, in some embodiments, a cruciatenotch or dovetail mechanism may be used, but may also act as astress-riser.

The tibial component 100 shown in FIGS. 1 through 3 may be part of a setof tibial trays of various standard sizes, or may be a patient-matchedtibial tray with certain geometries and/or other aspects of the traycustomized for a particular patient's anatomy. The tibial component 100shown in FIGS. 1 through 3 may be formed from bio-compatible materialstypically used to manufacture orthopaedic implants or may be formed fromother materials. The tibial component 100 shown in FIGS. 1 through 3 maybe formed using any desired or appropriate methodologies ortechnologies.

In some embodiments, the tibial component 100 may be manufactured usingSelective Laser Sintered technologies (“SLS”) or other free-formfabrication technologies, such as one or more of the EOS Laser-Sinteringsystems available from EOS GmbH of Munich, Germany. For instance, insome embodiments, the entire tibial component 100 may be formed as amonolithic implant (including any porous or other in-growth promotingsurfaces or materials). In other embodiments, portions of the tibialcomponent 100 may be formed using SLS technology and then additionalin-growth materials, surfaces, and/or treatments could be added orapplied to the implant. In other embodiments, electron beam meltingmethods or methods that use lasers to subtract or remove select portionsof material from an initially solid fin may be used. In otherembodiments, portions or all of the tibial component can be formed usingcasting or other technologies or methods. In some embodiments, anon-porous implant such as a tibial component may be formed using SLStechnologies and subsequently that implant may be subjected to acidetching, grit blasting, plasma spraying (e.g. of titanium oxide oranother metal to promote in-growth) or other treatments.

FIGS. 4 through 8 illustrate a modular stem 200 that may be used withthe tibial component 100 of FIGS. 1 through 3 in some, although notnecessarily all, embodiments. Indeed, in some embodiments, the tibialcomponent of FIGS. 1 through 3 will be used without any modular stem orotherwise incorporating any of the features or constructs of the modularstem shown in FIGS. 4 through 8. The modular stem 200 may connect to thestem portion 114 of the support member 110 of the tibial component ofFIGS. 1 through 3 via a taper fit mechanism (which may be furthersecured by a screw or other fastener in some embodiments). In otherembodiments, other mechanical attachment mechanisms may be employed, or,in still other embodiments, the stem is not modular but an integral partof the tibial component.

The embodiment of the modular stem 200 shown in FIGS. 4 through 8includes an inner core 210 from which a plurality of flutes 212 extend.In some embodiments, the inner core 210 has a tapered, conical or pressfit geometry positioned and oriented for where it is most likely (atleast in some cases) to encounter “harder” bone, and the flutes 212 arepositioned where they are most likely to encounter “softer” bone. Insome embodiments the general shape of the modular stem 200 facilitatesimplantation in a relatively close orientation and position to apre-defined orientation and position.

As shown in FIG. 6, the inner core 210, in some embodiments, may beslightly tapered and/or define a somewhat conical shape. Conicalfeatures such as this one (whose axes, at least in some embodiments, maybe directed generally parallel to the direction of load application) maybe beneficial because, in some uses, they may convert what otherwisewould be a purely compressive load into a compressive load that also hasa transverse component (i.e. a direction of which could becharacterized, at least in some embodiments, as orthogonal to thedirection of the compressive load). In some embodiments, this may bebeneficial in preventing bone immediately adjacent to the implant frombeing shielded from loading, at least for some of the time. In somecases, bone that is shielded from loading could remodel, resorb orotherwise degrade, resulting in a poor quality bone-implant interface.The tapered or conical shape of the modular stem 200 may also facilitatethe prevention of subsidence or migration. The tapered or conical natureof the inner core 210 may also facilitate a press-fit type interfacebetween the implant and bone. In the embodiment shown, a distal tip 214of the inner core is rounded.

As shown in FIGS. 4, 5, and 7, several flutes 212 extend radially fromthe inner core 210 of the modular stem 200. In the particular embodimentshown, the flutes 212 extend in a radially symmetric pattern such thatthe apexes of the flutes 212 are parallel to a central axis CA of theinner core 210. In other words, although the inner core tapers, theapexes of the flutes extend along a virtual cylinder. In otherembodiments, the apexes of the flutes may also taper as they extendtowards the distal tip of the stem; although, in at least some of theseembodiments, the flutes do not taper as much as the inner core. Because,at least in some embodiments, the inner core tapers to a greater degreethan the apex of the flutes, the flutes will “protrude” from the stem toa greater extent at distal portions of the stem than at proximalportions of the stem. Accordingly, in some embodiments, such a designmay pose less of a risk of fracturing the hard bone that is locatedproximate the proximal portions of the stem while still achievingfixation (rotational and/or translational) in the soft bone locatedproximate the distal portions of the stem. Additionally, in someembodiments, there may be less of a risk of deflection ormal-orientation or mal-position due to lack of or lessening of press-fitbetween the flutes and the hard bone.

As shown best in FIG. 8, in addition to the flutes 212 described in theprevious paragraph, the inner core of the modular stem may also includesecondary/smaller fluting 212′ extending therefrom. In some embodiments,the secondary fluting 212′ may be rounded or sharp, and may furtherfacilitate a tight fit with the surrounding bone, while, because theyare smaller, lessening the chance of tibial pain. In some embodiments,the fluting is radially symmetric and facilitates insertion of the stem200 to follow a pilot hole. FIG. 8 shows fluting useable in someembodiments of modular stems in which the stem 200 has fluting (or atleast primary fluting) that is spaced 120 degrees apart.

In some embodiments, the fluting is not radially symmetrical, butinstead exhibits planar symmetry. Planar symmetry may allow, in someembodiments, matching of the fluting to the support member geometry of atibial component. In some embodiments, the fluting is not radicallysymmetrical and is instead “handed” and specific for left or righttibias to accommodate particular or expected locations of hard and softbone. In some embodiments, patient matched technologies could beemployed to customize the fluting to the hard vs. soft bone distributionof the specific patient.

In some embodiments, the fluting may be tapered. In some embodiments,the “soft bone flutes” may be designed in such a way that over smallsections, they may be lower than the “hard” bone flutes. In someembodiments, the “soft” bone flutes could be parallel to the “hard” boneflutes but become tangentially wider to increase their effectiveness insoft bone. In some embodiments, the flutes could be discontinuous. Insome embodiments, the flutes could be made of a material different thanthat of the rest of the stem. In some embodiments, portions of the stemcould be porous coated or have surface finishes applied.

FIGS. 9-11 illustrate alternative possible support member shapes. Forexample, in FIGS. 9 and 10, there are two branches 310 (or arms orwings) of the support member 300. In FIG. 9, the branches 310 are angledrelative to one another, but in FIG. 10 the branches 310 aresubstantially aligned with one another. In FIGS. 11 and 12, the supportmember 300 has three branches or arms 312. Fewer or greater numbers ofbranches are possible.

As illustrated in FIGS. 12, 13 and 14, the tibial tray 410 and supportmember 420 may be modular and may have a male/female arrangement.Although in the figures the stem portion 420 is shown to have a femaleportion and the tibial tray 410 is shown to have a male portion, thesecould be reversed. In the embodiment depicted in FIG. 13, the tibialtray 410′ has a shoulder 430 that engages a ledge 440 of the stemportion 420′. The shoulder/ledge arrangement allows force to betransferred from the tibial tray 410′ to the stem portion 420′. Theshoulder/ledge arrangement also provides clearance or a gap between thetibial tray 410′ and the stem portion 420′ which may be used forvisualization and/or as a guide in revision surgery. Further, the areabetween the tibial tray 410′ and the stem portion 420′ may be used by asurgeon to separate the components in revision surgery. The shoulder 430also may provide a porous surface area for bone in-growth. As best seenin FIG. 13, the stem portion 420′ may engage in a taper lock with aportion of the tibial tray 410′.

FIG. 15 shows one embodiment of a tibial component 500 having a porousbead coating. The porous bead coating mimics the bumpy outer surfacegeometries and profiles of clinically-successful porous beads, with theroughness and porosity of a desired trabecular substrate. The porousbead coating may be applied to one or more of the following: theinferior surface of the tibial tray, the support member, the stemportion, the arms, the modular stem, or the modular stem flutes. Otherlocations are possible.

FIGS. 16-19 illustrate possible alternative embodiments of the supportmember. In FIG. 16, there is a support member 600 having openings orwindows 610. The support member 600 has a “wing-like,” two-sided “vane”shape with arcuate longitudinal sides. FIG. 17 illustrates a supportmember 700 with opening 710. The support member 700 has a general“I-beam” shape. FIG. 18 illustrates a support member 800 with openings810. The support member has a four-sided “vane” shape with linearlongitudinal sides. In FIG. 19, there is a support member 900 havingopenings or windows 910. The support member 900 has a corrugated“wing-like,” two-sided “vane” shape with compound arcuate longitudinalsides. Of course, other variations are possible.

Referring now to FIGS. 20-25, further embodiments to provide componentshaving porous beaded coatings and methods for their manufacture. Becauseimplants and natural bone usually have different degrees of flexibility,uneven stress distributions may occur. Consequently, when an implant isloaded, there is generally some relative movement at the interfacebetween the bone (more compliant) and the implant (more rigid). Manyimplants thus employ an intermediate material such as bone cement toreduce the amount of relative movement; however, cementless implants mayrely on relative roughness to achieve the same goals.

Historically, small spherical beads, bundles of thin wires, andthermal-sprayed metal have been used to produce the friction necessaryto reduce the amount of relative movement. Optionally, screws and/orpress-fit features may improve the fixation of implant to bone. Suchtechnologies are generally accepted by the orthopedic surgeon community.However, the geometric nature of these coatings limits the location andsize of their porosity. Newer technologies, such as those that employasymmetric beads or metallic foams have improved the location and sizeof porosity, but they are difficult to manufacture with favorablesurface textures. Remedies have included placing hatch lines into thesurface of an already porous coating (e.g., via machining). Other poroussurfaces have been manufactured having sharp protrusions at amicroscopic level. These protrusions can cause problems when there iseven a small amount of relative movement between the bone and implant.The sharper protrusions can dig into the bone and create bone particlesor can break off from the implant and create wear particles at theimplant-bone interface. In addition to loosening the attachment betweenthe implant and bone, these loose particles can cause harmfulcomplications.

The shortcomings of previous porous surfaces are addressed by providingan implant having a surface that is textured with numerous bluntprotrusions on a macroscopic level and has a porous structure on amicroscopic level. The blunt protrusions create friction that reducesthe amount of relative movement between an implanted component andsurrounding bone. The porosity allows the surrounding bone to grow intothe implant, and the lack of relative movement between implant and bonefacilitates this ingrowth.

A consideration in designing and creating a porous implant having bluntprotrusions is the size and density of the protrusions. The protrusionscreate an area on which the bone initially contacts an implant. If theprotrusions are too large or spaced too far apart, the majority of theimplant's surface area between the protrusions will be too far from thebone for the bone to grow into the implant, and the bone may be unableto create a solid interface with the implant. In contrast, if theprotrusions are too small or located too close together, their effectwill be minimal and an implant may encounter the same problems as priorimplants with smoother surfaces or surfaces composed of manyconcentrated sharp protrusions. An ideal surface contains protrusionsthat are large enough to create the needed friction between the bone andimplant and still small enough to still allow for a high degree of boneingrowth into the porous surface. The protrusions may be any suitableheight, and preferably are between about 50 μm and about 2000 μm. Forcertain applications, it may be preferable to limit the protrusionheights to between 200 μm and 400 μm to achieve the desired level offriction and ingrowth with surrounding bone.

Protrusions on a surface of an implantable component may be any suitableshape or profile desired for a general or specific application of thecomponent. In certain embodiments, each surface protrusion may be a bumpshaped as a portion of a sphere above the surface of the implant.Protrusions may also be shaped like wires or any other suitablefeatures, including features common to cementless implants.

Referring now to FIG. 20, an orthopaedic implant 1000 has a poroussurface that mimics the bumpy outer surface geometries and profiles ofclinically-successful porous beads, with the roughness and porosity of adesired ingrowth interface. The surface of implant 1000 is textured byblunt protrusions 1010, which are shaped substantially as hemisphericalbumps. The protrusions 1010 are sized and spaced to create desirablefriction that reduces movement of the implant 1000 relative tosurrounding bone while allowing the surrounding bone to growsubstantially into the porous protrusions 1010 and porous surface area1012 between the protrusions. In addition to the protrusion heightsdiscussed above, the spacing and density of protrusions 1010 affect theamount of friction and bone ingrowth created. Any suitable density ofprotrusions 1010 may be used for an implant, and the protrusionspreferably occupy between about 10% and about 60% of the surface. Theprotrusions may be concentrated to a density of between about 0.25beads/mm² and about 6 beads/mm².

Improved implants, such as the implant 1000 of FIG. 20, may be formed byany suitable approach, and may be formed using one of the following fourmethods.

A first method includes the steps of: 1) providing a mold having anegative impression of a porous beaded surface, 2) providing an implantsubstrate, which may be solid or porous, to be coated, 3) interposingsmall asymmetric particles between the implant substrate and said mold,and 4) applying a pressure and/or an elevated temperature to the mold,implant substrate, and small asymmetric particles to create a“green-state” implant (i.e., ready for full sintering) or a finalimplant (sintered), the implant having a roughened porous coating withan outer surface geometries and profiles mimicking a clinically-provenporous beaded structure with the roughness and porosity of a desiredtrabecular structure.

A second method includes the steps of: 1) creating a 3D model simulatingan outer surface profile of a porous beaded implant, 2) creating a modelof an implant substrate volume, 3) applying the 3D model simulating anouter surface profile of a porous beaded implant to the 3D model of theimplant substrate volume to create a bumpy pre-form volume, 4) applyingan algorithm to fill the bumpy pre-form volume with a desiredinterconnected porous or otherwise reticulated structure to create aporous implant model, and 5) creating an implant having a roughenedporous texture with an outer surface profile geometry mimicking aclinically-proven porous beaded structure using the implant model in arapid-manufacturing process.

A third method includes the steps of: 1) providing a mold of an implanthaving an inner surface mimicking a negative image of an outer surfaceprofile geometry of a porous beaded surface, 2) providing a plurality ofsmall asymmetric particles, 3) placing the plurality of small asymmetricparticles into the mold, and 4) applying a pressure and/or an elevatedtemperature to the mold and/or small asymmetric particles to create a“green-state” implant (i.e., ready for full sintering) or a finalimplant (sintered), the implant having a roughened porous texture withan outer surface profile geometry mimicking a clinically-proven porousbeaded structure.

A fourth method includes the creation of a beaded surface on a foamcomponent during the precursor step of making a metallic foam, themethod comprising the steps of: 1) providing a mold of an implant havingan inner surface mimicking a negative image of an outer surface profilegeometry of a porous beaded surface, 2) loading one or more foamingagents into the mold, 3) creating a porous foam component (e.g.,polymeric, polyurethane) in the general shape and/or size of saidimplant, which has an outer surface geometry mimicking an outer surfaceprofile geometry of a porous beaded surface, 4) removing the porous foamcomponent from the mold, 5) applying a binder or binding agent to theporous foam component, 6) applying a plurality of small symmetric orasymmetric particles (or a combination thereof) to the porous foamcomponent having a binder or binding agent thereon, 7) subjecting theporous foam component having binder or binding agent and particlesthereon to an elevated temperature to sinter the particles togetherand/or burn out the foam component to form a “green-state” implant(i.e., ready for full sintering) or a final implant (sintered), theimplant having a roughened porous texture with an outer surface profilegeometry mimicking a clinically-proven porous beaded structure. Implanthas a bumpy outer surface profile and geometries mimicking aclinically-proven porous-beaded structure.

The substrate forming at least an outer portion of the implant may be abulk porous, reticulated structure resembling a trabecular structure.One or more core portions or outer surface portions of the implant maybe solid (e.g., a portion of the implant may be configured forarticulation with another implant component). The implant may alsoinclude one or more solid internal portions. For example, implant 1000shown in FIG. 20 may include a solid structural portion on the interiorof the implant. The structural portion may be a single solid area ormultiple solid areas on the interior of implant 1000 that provide aseries of structural ribs to add support to the implant. The solidinternal structure may have any suitable shape and configuration, suchas a structural lattice similar to rebar in concrete. Illustrative butnon-limiting examples areas where the internal structure may be desiredinclude areas around screw holes, the equator region of an augment, orany other suitable area. In some embodiments, a polymer foam could bemelted or burned to have the shape of beads—or the foam could bepolymerized on a bead-shaped subsurface resulting in the end-producthaving a bead-shaped surface.

For rapid-manufacturing technologies, the bead surface geometries andprofile could be created virtually and subtracted out from a bulk porousentity or virtual beads could be created and combined with a porousentity. It is the general intent, in some, but not necessarily all,embodiments that the end-product be homogenous. Alternate embodiments ofimplants may include surface profiles that mimic metallic wire bundlesor the peaks and valleys of a thermal sprayed coating. Once a virtualmodel of the desired geometry is created using modeling software, animplant component having the desired surface profile can be createdusing any suitable rapid manufacturing techniques. For example, theporous implant can be created using 3D printing technology that usespowdered metal to “print” the modeled implant. In such an approach, afoam may be created having a surface profile that includes protrusions,such as protrusions 1010 in FIG. 20, and the profiled foam may then befilled in with powdered metal to create a porous microstructure with theprofiled surface. A foam that does not contain the protrusions may alsobe used to create the porous microstructure with powdered metal, and thedesired surface profile with protrusions can then be stamped into thesurface of the porous metal implant.

Advantages of implants manufactured this way are that they containintegral porosity with the initially bone-engaging surface profile ofclinically-proven porous beads. In other words, the same featuresproviding the traction needed between bone and implant are the samefeatures providing a surface for bone to grow into and around for arigid and enduring fixation surface. As non-limiting examples, Tables Aand B show some examples of potentially suitable bead density (spacing),and diameter.

Table A. Chart of number of beads in selected area and average andstandard deviation of bead diameter of 50 beads on a shell used with theBirmingham Hip® Resurfacing system available from Smith & Nephew, Inc.in at least 3 fields of view (SEM, Jeol, Japan)

TABLE A Chart of number of beads in selected area and average andstandard deviation of bead diameter of 50 beads on a shell used with theBirmingham Hip ® Resurfacing system available from Smith and Nephew.Inc. in at least 3 fields of view (SEM, Jeol, Japan) Beads in 6.4 × 4.8mm area Bead Diamter (mm) 11 Average D 1.24 20 Std D 0.12 20

TABLE B Percent solid for typical beaded product for bone ingrowth.Product Company Implant Type Percent Solid CoCr ROUGHCOAT Smith andProfix ® Femoral 46.3% (2-layer) Nephew CoCr Porocoat DePuy LCS ® KneeFemoral 46.5% (3-layer) CoCr Porocoat DePuy AML ® Stem 50.2% (3-layer)Ti ROUGHCOAT Smith and Synergy ™ Stem 51.9% (2-layer) NephewWherein, “percent solid” is a 2D measurement of bead density produced bytypical metallographic techniques based on the test method disclosed inASTM F1854, entitled “Standard Test Method for Stereological Evaluationof Porous Coatings on Medical Implants,” which is incorporated byreference herein in its entirety.

FIG. 21 shows a coating volume 1510 having spherical bead volumes 1512placed therein, such that the spherical bead volumes 1512 protrude fromthe coating volume 1510 to form a second coating volume mimicking aspherical bead profile. Alternatively, solid spherical beads may becombined into a porous coating. To create the coating volume 1510, twosoftware models can be created and then merged to form the final modelof the porous volume with the profiled protrusion surface. A first modelof a macroscopic structure of the volume, including the plurality ofbead volumes 1512, can be created in modeling software, and may looksubstantially the same as the volume shown in FIG. 21.

A second software model can be created to produce the porous microscopicstructure desired for a macroscopic volume, such as the volume shown inFIG. 21. FIG. 22A shows a unit cell 1520 of an exemplary porousreticulated structure, which may configured to fill the coating volumemimicking a spherical bead profile. The unit cell 1520 is made up of acomplex structure of struts 1512. The arrangement of struts 1512 createsvoids 1514 within unit cell 1520, thus making the desired porousmicrostructure. The size and arrangement of struts 1512 can be varied tocontrol the number and size of voids 1514. By controlling the size andarrangement of the struts 1512, a desired amount and profile of theporous structure is achieved. FIG. 22B schematically illustrates aconglomeration of unit cells on a macroscopic level.

FIG. 23 shows a cross section of a coating volume 1530, which maycorrespond to coating volume 1510 of FIG. 21, mimicking a spherical beadprofile after the volume has been replaced with a reticulated structure(e.g., via a repeating unit cell such as unit cell 1520 in FIG. 22A inCAS software, or using any of the 4 methods described above). Thefinished coating volume 1530 exhibits both the profiled macrostructureand porous microstructure. The dotted lines in FIG. 23 outline thesurface profile of coating volume 1530 and show the protrusions thatcreate a bumpy surface that produces friction with bone when implanted.The microstructure of coating volume 1530, made up of a combination ofsolid structure 1532 and voids 1534, creates a porous implant into whichsurrounding bone can grow to fill in voids 1534 and create a solidmating of implant and bone.

FIG. 24 shows an SEM image 1540 taken at 25× magnification of thesurface of a part made by the disclosed method. Surface topography isnot apparent with this view. FIG. 25 is an SEM image taken 1550 at 50×magnification of the structure made with the disclosed method. Thestructures shown in FIGS. 24 and 25 exhibit the porous microstructurediscussed above with respect to coating volumes 1510 and 1530, and canbe created by merging a solid macrostructure with a porousmicrostructure model, such as the unit cell 1520 in FIG. 22A.

As a further non-limiting example, the following chart shows someadditional exemplary parameters that have proven to be useful forvarious embodiments. In the chart below, MVIL refers to Mean VoidIntercept Length, which is another way of characterizing the averagepore size, particularly in structures where the pore shapes and sizesare not uniform. On generally known definition of MVIL is “measurementgrid lines are oriented parallel to the substrate interface. The numberof times the lines intercept voids is used with the volume percent voidto calculate the mean void intercept length.”

Electron beam Direct metal laser Landon melting sintering (SLS)Structure (EBM) Eurocoating EOS (FIG. 4) Avg. Strut — 275-450 275-400Thickness (μm) (360) (340) Avg. Pore Size: MVIL 300-920* 450-690 — (565)(560) Average Pore  900-1300* 1310 ± 280  1970 ± 40  Pore Window — 370 ±100 830 ± 150 Size: (μm) Not 670-1340 600 ± 100 — Specified *(fine,medium, and coarse structures)

It is generally desirable to provide between about 60-85% porosity. Poresizes may generally range between about 50-1000 microns. In the aboveexample, the smallest pore size provided was about 300 microns, and thesmallest window was about 595 microns across at its largest diameter. Itwill be understood that this example is intended to be non-limiting andprovided for illustrative purposes only.

The systems, methods, and devices described herein to create implantshaving both a profiled macrostructure and a porous microstructure canallow a medical professional to utilize customizable, patient-specificimplants. A customized implant can be efficiently created using therapid manufacturing techniques discussed herein by merging two or moremodels of an implant and then printing the modeled component. This couldallow a medical professional, such as an orthopedic surgeon, to order animplant specific to a single patient, including modeling the size andshape of the implant to fit defects or other unique features of thepatient's anatomy. This process can also be automated by taking bonescans of the patient's anatomy or using other available medical imagingand modeling techniques to automatically create a 3D model to use forrapid manufacturing.

The ability to customize an individual implant also allows a medicalprofessional to adjust the detailed macrostructure and microstructure ofthe implant to fit the needs of a particular application. For example,an orthopedic surgeon can adjust the macrostructure of the implant byselecting the shape, height, density, or other characteristics ofprotrusions on the surface of the implant. The surgeon can alsocustomize the number and size of voids within the implant to achieve adesired porosity for the implant. In some embodiments, the surgeon mayalso select the configuration of the macrostructure of the implant. Forimplants that include internal solid portions for strength andstructure, the surgeon can customize the size and location of theinternal solid portions to provide the structure in certain non-uniformareas of the implant where increased strength is needed. Illustrativebut non-limiting examples areas where increased strength may be desiredinclude areas around screw holes, the equator region of an augment,connection sites of augments, augment areas that are thinner thanothers, or any other suitable area. The surface profile of the implantcan also be non-uniform if different areas of the implant requiredifferent levels of friction or surface area for a bone interface. Asurgeon may want a higher concentration of surface protrusions incertain areas of the implant, such as areas that experience higherlevels of stress, and a lower concentration of protrusions, or noprotrusions at all, in other areas.

Porous implants described herein allow for an implant to provide a goodcontact surface area and friction regardless of the quality of bone intowhich an implant is implanted. For example, patients who have softspongy bone may need features that are longer, and a lower number ofthose features. Patients with hard dense bone may require features thatare shorter, but a higher number of those features to create the samefixation in the bone. The specific requirements of a patient's anatomyand bone quality can be accommodated by the individualized designoptions provided by the porous implants described herein.

As various modifications could be made to the exemplary embodiments, asdescribed above with reference to the corresponding illustrations,without departing from the scope of the invention, it is intended thatall matter contained in the foregoing description and shown in theaccompanying drawings shall be interpreted as illustrative rather thanlimiting. Thus, the breadth and scope of the present invention shouldnot be limited by any of the above-described exemplary embodiments, butshould be defined only in accordance with the following claims appendedhereto and their equivalents.

What is claimed is:
 1. A tibial component, comprising: a tibial trayhaving a superior side and an inferior side; and a support memberconnected to the inferior side of the tibial tray, the support membercomprising a stem portion and at least three arms that each define anopening; wherein the inferior side includes a porous coating including aplurality of protrusions, the plurality of protrusions occupying between10% and 60% of an overall surface area of the inferior surface.
 2. Thetibial component of claim 1, wherein a portion of each of the openingsis defined by the stem portion, and wherein the at least three armscurve to connect to the inferior side of the tibial tray to form theopenings.
 3. The tibial component of claim 1, wherein each of the atleast three arms is angled relative to one another.
 4. The tibialcomponent of claim 3, wherein the at least three arms comprise no morethan three arms.
 5. The tibial component of claim 3, wherein the atleast three arms comprise four arms.
 6. The tibial component of claim 5,further comprising a plurality of pegs arranged about the four arms. 7.The tibial component of claim 6, wherein the plurality of pegs includefour pegs.
 8. The tibial component of claim 5, wherein each of the fourarms extends from a proximal end connected to the inferior side of thetibial tray to a distal end arranged opposite the proximal end, andwherein each of the four arms comprises a pair of planar surfaces thatextend parallel to one another from the proximal end to the distal end.9. The tibial component of claim 8, wherein the four arms cooperate atthe distal ends thereof to define an inferior-most tip of the supportmember.
 10. A tibial component, comprising: a tibial tray having asuperior side and an inferior side, the tibial tray further including apedestal extending from the inferior side thereof, the pedestal definingan inferior-most point of the tibial tray; and a support member coupledto the inferior side of the tibial tray, the support member comprising astem portion and at least two openings spaced from one another, thesupport member further including a pedestal-receiving passage having afirst opening arranged opposite an inferior tip of the support memberand a second opening arranged between the first opening and the inferiortip; and wherein the pedestal is sized for receipt in thepedestal-receiving passage of the support member so that the supportmember is removably coupled to the tibial tray, the first opening beingsized to receive a body of the pedestal that has a first width and thesecond opening being sized to receive a head of the pedestal that has asecond width smaller than the first width.
 11. The tibial component ofclaim 10, wherein the first opening is larger than the second opening.12. The tibial component of claim 10, wherein the head of the pedestalcomprises a threading which threadingly engages a correspondingthreading of the support member that extends from the second opening toa floor of the pedestal-receiving passage.